The present invention relates to a semiconductor memory device, and more particularly to a semiconductor memory device of a type in which electrically written information is erased by ultra-violet rays. The device is called as a UV-EPROM and its package has a window plate made of a material (e.g., quartz glass) transparent with respect to ultra-violet rays through which the irradiating rays are to be applied to a UV-EPROM chip housed within the package to conduct the erasing operation. When the device is not under the erasing operation, the window plate is covered by a shading sheet in order to prevent erasure of the stored information or maloperation of the device due to lights including ultra-violet rays. In the prior art, the shading sheet is made of an ordinary paper and a band film formed on the back surface of the paper and the sheet adheres to the surface of the window plate. The band film does not permanently fix the paper to the window so that the paper can be peeled from the window during the erasing operation. The ordinary paper has a high electrical resistivity of 10.sup.6 .OMEGA..multidot.cm or more and is generally opaque against lights, particularly to lights of 4000 .ANG. wave length or less including ultra-violet rays. In the semiconductor memory device of the prior art, the shading sheet as well as the window material has the high electrical resistivity and therefore, a large amount of electric charges are easily accumulated on the window plate when the upper portion of the package, that is, the window covered by the shading sheet contacts and collides with another insulating material such as another package or a magazine case in which many UV-EPROM's are installed. The accumulated charges induce a high electric field which is applied to the UV-EPROM chip positioned under the window to cause maloperation of the device. Possible measures to avoid such maloperation would be a very thick passivation film coated on the surface of the chip or a thin gold film of 1000 .ANG. thickness or less coated on the window plate to discharge the accumulated charges. However, in the former case, unfavorable cracks are easily produced in the thick passivation film, and in the latter case, sufficient discharge cannot be expected and a cost of the package becomes high because of the use of gold.